The present invention relates generally to wireless communications systems, and more specifically to a low-cost high performance multiple input multiple output (MIMO) wireless broadband communications system.
In recent years, there has been an increasing need for wireless communications systems capable of carrying broadband data. Such a need has arisen for a variety of reasons, including the difficulties that users often experience in obtaining high speed Internet access service in some remote areas, and the convenience that wireless systems generally afford to users wishing to set up communications links and networks accessible from locations within urban environments or from locations dispersed across significant geographical distances.
Initial attempts at providing wireless broadband services in point-to-point and point-to-multipoint applications have included deploying line-of-sight (LOS) wireless communications systems, in which a directional antenna is typically installed at one or more user locations within the line-of-sight of an antenna at a base station. Such LOS wireless communications systems have drawbacks, however, including the high cost of system installation. For example, whether or not a prospective user location has an unimpeded view to the base station can often be determined only after an installer has been dispatched to the site. For this reason, a successful installation is not always assured after one visit of the installer and may require multiple installer visits, thereby increasing costs. In addition, in the event the location of the base station changes, the directional antenna at the user location must normally be re-aimed at the new base station location, resulting in increased costs.
Such drawbacks of conventional LOS systems have given impetus to the development of non-line-of-sight (NLOS) wireless broadband communications systems such as multiple input multiple output (MIMO) wireless communications systems. For example, a MIMO wireless communications system typically includes a plurality of antennas at a transmitter location and a plurality of antennas at a receiver location. The transmitters typically transmit signals using known space-time coding and modulation techniques. Further, one or more receivers capture the transmitted signals, and employ signal processing techniques to decode and demodulate the signals to recover user data. The multiple antennas of the MIMO system can be deployed in an environment that includes numerous scattering objects such as buildings, trees, hills, automobiles, etc. The transmitted signals undergo multi-path propagation between the transmitters and the receivers while being scattered by the various objects within the environment. Such a multi-path environment allows multiple paths to be established between the transmitters and the receivers. By transmitting user data in parallel over these multiple paths, both increased data rates and higher spectral efficiencies can be achieved.
Conventional NLOS wireless communications systems also have drawbacks, however, in that they have generally been unable to provide the high levels of link availability, data throughput, and system performance that users of broadband services demand. This is because, in general, issues such as signal attenuation, signal fading, and channel dispersion have not been satisfactorily addressed in conventional NLOS wireless systems.
It would therefore be desirable to have a low-cost high performance wireless broadband communications system that avoids the drawbacks of the above-described conventional wireless communications systems.